1. Field of the Invention
The present invention relates to a printer which is used to print not only on regular stationery, but also on cartoon-board or thick, non-flexible printing material. More particularly, the printer equips a mechanism to automatically and continuously adjust inkjet clearance between an inkjet nozzle and a printing material surface for printing on thick, non-flexible printing material.
2. Description of the Related Art
Generally, an inkjet printer has a mechanism for injecting or spraying extremely fine ink droplets onto a sheet of paper to print characters, images or pictures. The printer adopting this kind of inkjet method equips an injection head having a plurality of tiny nozzles to spray the ink droplets directly onto the paper.
The ink contained in the nozzle is heated by a heating element, and expanded out of the nozzle for injection onto the paper.
In accordance with the characters, images or pictures to be printed, the injection head travels horizontally, and selectively operates the appropriate nozzles to print the intended characters, images or pictures. At this point, the injection head attached on the carrier is driven by a carriage motor, and the carrier travels horizontally, either rightward or leftward, along the horizontally extended carrier shaft.
The components of a typical inkjet printer consist of a line feed mechanism, a carriage mechanism, a home assembly, a friction roller assembly, a carriage drive motor, a line feed drive motor, etc. being assembled and installed onto a printer frame.
The line feed mechanism is comprised of a frame base assembly and feed rollers. The paper-feeding assembly feeds a sheet of paper toward the ink injection head, which is attached to the carriage of the carriage mechanism. The ink injection head is integrally assembled with an ink chamber and an ink cartridge.
The ink cartridge is usually replaceable. The injection head is placed at the bottom face of the ink cartridge, against the surface of a sheet of paper. When a sheet of paper arrives at the contacting point between the feed roller and the friction roller, the sheet of paper is picked up by the rollers. Then, the feed roller, driven by the line feed drive motor, passes the sheet of paper to the injection head for printing the characters, images or pictures on the paper. The printed paper is then discharged to the outside of the printer.
Because the quality of printing is affected mainly by the size and impacting force of the ink droplets on the paper, it is important to maintain the optimum clearance between the injection head and the paper surface. In order to achieve the highest print quality, the injection head must be properly positioned to maintain optimum clearance for injecting the ink droplets onto the paper. If the actual print injection clearance is less than or greater than the optimum clearance, print quality would be adversely affected, as would be evident in the resulting deformation of pictorial elements brought about by inappropriate impacting force and size of ink droplets onto the paper.
Even when the ink injection head is properly set for optimum clearance, print quality may vary due to the varying thickness of printing materials.
Korea Patent No. 1998-0000949 discloses a printer having an adjustable inkjet clearance for obtaining optimum print quality. The conventional inkjet printer comprises a mechanism for automatically adjusting injection head clearance according to the paper thickness as detected with sensing devices.
Because the conventional printer adjusts injection head clearance by way of a cam, the adjusting range is limited; although it can print on paper that is slightly thicker than standard stationery, letter envelope, label, etc., it cannot print on cartoon-board, or thick, non-flexible printing material such as rigid cartoon paper or materials such as plastic, wood board, CDs, books, etc.